Photometry

Abstract

Photometry is the process of determining intensity or magnitude of or within the original object. It most commonly involves measurements of point sources or near-point sources like stars and planets, but it can also involve measuring the integrated intensities or magnitudes of more extended objects. Any of the detectors discussed in Chapter 9 can be used for photometry, the CCD and p-i-n photodiode are however the most straightforward because they have linear responses, and their outputs can be converted directly into magnitudes using Eq. (8.5). The eye and the photographic emulsion are non-linear detectors and their responses are therefore more complex to convert into magnitudes. The visual estimation of magnitude having already been discussed in Chapter 8, we shall consider photographic photometry further below.